There's a whole field of social science dedicated to the study of group dynamics and collective behavior. Within this field, researchers investigate various aspects of a group. For example, some researchers study cohesiveness, which refers to all of the forces that cause individuals to remain in groups. Others study participation, which looks at differences not only in the amount of participation among group members, but also the manner, style or tone in which they participate. And, of course, many collective behaviorists study communication within groups. They want to know who does the talking, for how long and how often.

Although this research has revealed much about how crowds behave, it has not shed any light, at least not directly, on the topic of the silence of "20 minutes after the hour." It has provided some indirect evidence that sudden silences in crowds might be little more than superstition. For example, there is a commonly held myth that all crowds are unanimous. Unanimity manifests itself when everyone in a crowd acts in unison. Clark McPhail, author of "The Myth of the Madding Crowd," suggests that such unanimity in crowds rarely happens. According to McPhail's landmark book, people remain stubbornly individual, even when they are surrounded by others. If this is the case, it would seem sudden silences, which would require a crowd to be unanimously silent, would be rare.

But let's accept, just for a moment, that crowds do fall silent on occasion. Let's also put aside the question of whether or not the silences occur at exactly 20 minutes after the hour. Are there physiological or psychological reasons why silence in a group might be necessary? Does silence help the group as a whole or the individuals within the group? Science is able to provide some clues to these questions.

Let's start first with a physiological explanation. Over the years, scientists have tried to understand the physiological mechanisms in rats exposed to a high degree of stress. In one experiment, researchers exposed rats to a buzzer sounding for six out of 30 seconds, seven hours a day for 35 days. The animals in this group suffered from high blood pressure and paced their cages nervously. Animals in the control group, which lived in quiet cages, had markedly lower blood pressure and did not pace nervously.

Now let's consider a 2005 study from the University of London that aimed to understand the psychological impact noise might have. In this experiment, researchers studied 2,800 children in 89 schools. Some of the schools were located next to airports, while others were not. Children exposed to high levels of aircraft noise had much poorer reading skills than children in quieter neighborhoods. Researchers used the term "cognitive fatigue" to describe why reading skills might suffer in children living in noisy environments. In such conditions, their long-term memory is interrupted, and they simply stop paying attention.

What do these studies suggest about sudden silences? Perhaps silence in a crowd is a protective mechanism. It keeps the blood pressure of individuals low and reduces cognitive fatigue. This maintains the health of each member of the group, which, ultimately, maintains the health of the group itself.